The goal of the proposed research is to develop new dynamic chest imaging techniques based on a digital radiographic system that has a large image intensifier (57-cm)-TV system as the x-ray detector. The new techniques are distinctly different from existing chest imaging techniques in that they utilize the unique physical characteristcs of the digital system; a large area detector, effective scatter rejection, rapid image acquisition, and computerized image processing. These methods have the potential to improve diagnostic accuracy for detection of pulmonary diseases at reduced patient exposure and risk, as well as at a reduced cost. The specific aims of this research include: (1) studies of pulmonary ventilation with non-radioactive xenon gas as the contrast medium, and (2) detection of pulmonary embolism by digital subtraction radiography with or without contrast injection. The application of dynamic digital techniques to chest radiography can provide quantitative and dynamic data for evaluation of pulmonary ventilation and pulmonary embolism. Initially, the basic imaging parameters of dynamic chest imaging will be optimized by using Monte Carlo simulation studies based on patient dose, detective quantum efficiency of the image intensifier, contrast sensitivity, and antiscatter techniques. A beam equalizing filter device will be developed for reducing the dynamic range of the chest radiographs. Secondly, phantom studies will be applied to determine the imaging characteristics of the new techniques. Thirdly, computer algorithms will be developed for quantitative analysis of the dynamic information recorded in the images. Finally, preliminary clinical studies will be performed to demonstrate the feasibility of the dynamic imaging techniques.